1. Field of the Invention
This invention relates to a method for the treatment of a solution of tertiary butyl hydroperoxide in tertiary butyl alcohol to be used as a feedstock in a molybdenum catalyzed olefin epoxidation process in order to inhibit precipitation of the molybdenum catalyst during the epoxidation reaction. More particularly, this invention relates to a method for the partial removal of acidic impurities such as formic acid, acetic acid, isobutyric acid, etc., from a solution of tertiary butyl hydroperoxide in tertiary butyl alcohol to be used as a feedstock in an olefin epoxidation process, such as a process wherein propylene is catalytically reacted with tertiary butyl hydroperoxide in solution in tertiary butyl alcohol in the presence of a catalytic amount of a soluble molybdenum compound in order to inhibit precipitation of the molybdenum catalyst during the epoxidation reaction.
More particularly, this invention relates to a method for the pretreatment with calcium hydroxide and/or calcium oxide of a distillation fraction to be used as a feedstock in a molybdenum catalyzed olefin epoxidation process wherein tertiary butyl hydroperoxide is reacted with an olefin, such as propylene, in solution in tertiary butyl alcohol in an epoxidation reaction zone in order to provide propylene oxide and additional tertiary butyl alcohol, the distillation fraction comprising a solution of tertiary butyl hydroperoxide in tertiary butyl alcohol contaminated with acidic impurities such as formic acid, acetic acid, isobutyric acid, etc., the improvement of the present invention comprising the pretreatment of the distillation fraction with an amount of calcium oxide and/or calcium hydroxide sufficient to partially precipitate the acidic impurities and the removal of the precipitate, whereby, when the thus-treated distillation fraction is used as a feed stock in the epoxidation reaction process, the precipitation of the molybdenum catalyst during the epoxidation reaction is substantially inhibited.
2. Background of the Present Invention
When an olefin epoxide, such as propylene oxide, is to be prepared from the corresponding olefin, such as propylene, by reacting the olefin in organic solvent solution with tertiary butyl hydroperoxide in the presence of a soluble molybdenum catalyst, it is conventional practice to prepare the hydroperoxide feedstock by the non-catalytic or catalytic oxidation of isobutane with oxygen in an oxidation reaction zone to provide an oxidation reaction product comprising unreacted isobutane, tertiary butyl hydroperoxide, tertiary butyl alcohol and oxygen-containing impurities.
It is also conventional practice to remove the unreacted isobutane from the initial oxidation reaction product by distillation and to use the remaining distillation product fraction (normally a bottoms fraction) as the feedstock for the molybdenum-catalyzed reaction of an olefin with the tertiary butyl hydroperoxide. This is advantageous because the tertiary butyl alcohol present in the initial oxidation reaction product serves as a solvent for the peroxidation reaction and because the co-product of the peroxidation reaction is tertiary butyl alcohol, derived from the tertiary butyl hydroperoxide reactant. As a consequence, product work-up is simplified because there is no need to use an extraneous solvent. Also, tertiary butyl alcohol is widely used in motor fuels to enhance the octane characteristics of the motor fuels.
3. Prior Art
It is known to react propylene with tertiary butyl hydroperoxide in the presence of a soluble molybdenum catalyst to provide a reaction product comprising propylene oxide and tertiary butyl alcohol. See, for example, Kollar U.S. Pat. No. 3,350,422, Kollar U.S. Pat. No. 3,351,635, and Russell U.S. Pat. No. 3,418,340.
It is also known to prepare soluble molybdenum catalysts to catalyze the reaction as disclosed, for example, in Bonetti et al. U.S. Pat. No. 3,480,563, Shum et al. U.S. Pat. No. 4,607,113, Marquis et al. U.S. Pat. No. 4,626,596, Marquis et al. U.S. Pat. No. 4,650,886, Marquis et al. U.S. Pat. No. 4,703,027, etc.
It has also been recognized in the prior art that it is desirable to conduct the molybdenum-catalyzed reaction between the propylene and tertiary butyl hydroperoxide in a reaction medium of reduced acidity. Thus, Kollar U.S. Pat. No. 3,350,422 states that it is advantageous to use basic substances such as alkali metal compounds or alkaline earth metal compounds with the catalyst in order to reduce acidity. Similar disclosures are found in Kollar U.S. Pat. No. 3,351,635 and Russell U.S. Pat. No. 3,418,340.
Wu et al. U.S. Pat. No. 4,217,287 discloses a process wherein the reaction is conducted in the presence of barium oxide in order to "stabilize the catalyst". Becker U.S. Pat. No. 4,262,143 discloses a related process for preparing ethyl benzene hydroperoxide. The ethyl benzene hydroperoxide is prepared by the oxidation of ethyl benzene with molecular oxygen in the presence of a small amount of a hydroxide or salt of sodium or potassium. In another process, Iwaki et al. U.S. Pat. No. 4,293,720 discloses a liquid phase process for the preparation of aromatic peroxides by the liquid phase oxidation of an aromatic compound containing a secondary alkyl group with molecular oxygen in the presence of a basic aqueous solution of a copper compound catalyst which also contains cupric carbonate and an alkali metal carbonate and/or an alkali metal bicarbonate.
Kollar U.S. Pat. No. 3,860,662 is directed to an improvement in his basic process relating to the recovery of alcohols from the reaction product, which product is stated to be of an acidic nature, wherein a basic material such as an alkali metal or alkaline earth metal compound is added to the reaction mixture. Kollar U.S. Pat. No. 3,947,500 discloses a method for treating the reaction product formed by the reaction of an organic hydroperoxide with an olefin wherein an organic alcohol is formed as a by-product. It is stated that the alcohol tends to dehydrate and that to at least partially overcome this problem the oxidation reaction product is treated with an alkali metal or an alkaline earth metal compound. Kollar states that the alkali metal or alkaline earth metal compound can be added to the epoxidation reactor or to the reaction product.
Sorgenti U.S. Pat. No. 3,573,226 discloses a method wherein a molybdenum-containing catalyst solution is prepared by incorporating metallic molybdenum into the distillate bottoms fraction of an epoxidation reaction product followed by heating of the resultant mixture in order to form a soluble molybdenum-containing reaction product which can be used to catalyze the epoxidation reaction.
The molybdenum-catalyzed epoxidation of alpha olefins and alpha substituted olefins with hydroperoxides less stable than tertiary butyl hydroperoxide may be accomplished according to U.S. Pat. No. 3,862,961 to Sheng, et al. by employing a critical amount of a stabilizing agent consisting of a C.sub.3 to C.sub.9 secondary or tertiary monohydric alcohol, such as tertiary butyl alcohol. Citric acid is used to minimize the iron-catalyzed decomposition of the organic hydroperoxide without adversely affecting the reaction between the hydroperoxide and the olefin in a similar oxirane producing process taught by Herzog in U.S. Pat. No. 3,928,393. The inventors in U.S. Pat. No. 4,217,287 discovered that if barium oxide is present in the reaction mixture, the catalytic epoxidation of olefins with organic hydroperoxides can be successfully carried out with good selectivity to the epoxide based on hydroperoxide converted when a relatively low olefin to hydroperoxide mole ratio is used. The alpha-olefinically unsaturated compound should be added incrementally to the organic hydroperoxide.
Selective epoxidation of olefins with cumene hydroperoxide (CHP) can be accomplished at high CHP to olefin ratios if barium oxide is present with the molybdenum catalyst as reported by Wu and Swift in "Selective Olefin Epoxidation at High Hydroperoxide to Olefin Ratios," Journal of Catalysis, Vol. 43, 380-383 (1976).
Maurin U.S. Pat. No. 3,931,076 is directed to a method for recovering molybdenum catalyst values from a peroxidation reaction product for recycle. Maurin discloses one of three techniques. In accordance with the first embodiment, the residue fraction is calcined to provide molybdenum trioxide which is then used to prepare a soluble molybdenum compound by reaction with aqueous ammonia. In a second embodiment, the molybdenum-containing fraction is treated with aqueous ammonia without calcining to form an ammonium molybdate which is treated with a polyalcohol to give a molybdic ester. In a third embodiment, the molybdenum-containing fraction is treated with gaseous ammonia in order to form an ammonium molybdate precipitate which can be recovered by filtration.
As can be seen by the foregoing, when it is desired to reutilize the molybdenum catalyst initially used to catalyze the epoxidation reaction between an olefin such as propylene and a hydroperoxide such as tertiary butyl hydroperoxide, the used molybdenum catalyst is normally concentrated in a distillation bottoms fraction which contains other impurities such that direct recycle, without treatment, is normally impractical.
Harvey U.S. Pat. No. 3,449,217 is directed to a process for the recovery of tertiary butyl hydroperoxide from a mixture comprising tertiary butyl hydroperoxide, tertiary butyl alcohol and organic acids and esters resulting from the liquid phase oxidation of isobutane by a process which minimizes hydroperoxide decomposition. This is done by accomplishing the distillation while the product has an effective pH of below about 9. The patentee teaches the treatment of the reactor effluent with a neutralizing agent such as an alkali metal or an alkaline earth metal hydroxide.